Abstract
BackgroundBiological invasions affecting rocky intertidal zonation patterns, yield information on species interactions. In the Bay of Antofagasta, northern Chile, the non-indigenous tunicate Pyura praeputialis, originally from Australia, has invaded (in the past century or so) and monopolized a major portion of the mid-intertidal rocky shore, displacing upshore the native mussel Perumytilus purpuratus. In Antofagasta the tunicate is subjected to intensive exploitation. Monitoring protocols show that in the past 10 years Antofagasta's tunicate population has experienced a drastic decline, affecting the intertidal zonation pattern.Methodology/Principal FindingsA 12.5 km of coastline, on the southern eastern shore of the Bay of Antofagasta, was studied. Eight sites were systematically (1993–1994) or sporadically (2003–2014) monitored for the seaward-shoreward expansion or reduction of the tunicate Pyura praeputialis, and native mussel and barnacle bands. A notable reduction in the mid-intertidal band of P. praeputialis and a seaward expansion of the mussel, Perumytilus purpuratus, and barnacle bands was observed. We suggest that the major cause for the decline in the tunicate is due to its intensive exploitation by rocky shore Pyura-gathers. The rate of extraction of tunicates by professional Pyura-gathers ranged between 256–740 tunicates hour−1. Between 2009–2014 the density of professional Pyura-gather ranged between 0.5–4.5 km−1 per low tide. Hence, 10 professional Pyura-gathers working 1 h for 10 low tides per month, during 6 months, will remove between 307–888 m2 of tunicates. A drastic decline in tunicate recruitment was observed and several P. praeputialis ecosystems services have been lost.Conclusion and SignificanceIn Antofagasta, the continuous and intensive intertidal gathering of the invasive tunicate Pyura praeputialis, has caused a drastic reduction of its population modifying the zonation pattern. Thereby, native mussel Perumytilus purpuratus has regained its ecological center in the intertidal zone. We recorded a Pyura recruitment failure and loss of ecosystem services.
Highlights
One of the main goals of ecology is to understand the mechanisms and processes responsible for the abundance and distribution patterns of species in their environment, which includes humans
Thereby, native mussel Perumytilus purpuratus has regained its ecological center in the intertidal zone
Our study area of 12.5 km is located along the southeastern shore of the bay: i) Asociacion de Automovilistas de Antofagasta (AAA, 23u429500S; 70u259430W), ii) Llacolen (23u429490S; 70u269000W), iii) El Way (23u440120S, 70u269 280W), iv) Caleta Coloso (23u459230S; 70u279310W), v) Minera Escondida Limitada at Punta Coloso (MEL, 23u459170S; 70u289020W), vi) Outside MEL (23u459390S; 70u289210W), vii) El Lenguado (23u469120S; 70u289280W), and viii) La Mina (23u460420S; 70u299030W) (Fig. 1)
Summary
One of the main goals of ecology is to understand the mechanisms and processes responsible for the abundance and distribution patterns of species in their environment, which includes humans. Rocky intertidal food-gathering by artisan or subsistence fishers affecting populations of carnivore keystone species, herbivores and primary producers, leading to the modification of population, community, trophic web and alternative ecological states, have been reported for central and southern Chile [1,2,3,4,5,6,7], South Africa [8,9,10] and Australia [11]. In these reports the ecological role played by humans, as resource extractors, has been characterized as extremely efficient and corresponding to a super-keystone species [12]. Monitoring protocols show that in the past 10 years Antofagasta’s tunicate population has experienced a drastic decline, affecting the intertidal zonation pattern
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